1. Field of the Invention
The present invention relates to a photosensitive composition and a method for forming a pattern using the same.
2. Description of the Related Art
A photoresist has been used in the industrial field of electronic devices requiring various kinds of minute processing, such as a semiconductor integrated circuit including an LSI. As an exposing apparatus used for forming a pattern of the photoresist, a reduced projection mask aligner, which is generally referred to as a stepper, has been used. Examples of a light source used in the apparatus include the g line (wavelength: 436 nm), the h line (405 nm) and the i line (365 nm) of a mercury lamp, and KrF (248 nm), ArF (193 nm) and F2 (157 nm) as an excimer laser. Exposure with an electron beam and an ion beam also attains high resolution processing owing to the short wavelength thereof and can directly form a pattern. Therefore, electron beam lithography is considered as being important, and a resist capable of being used therefore is demanded.
According to the progress in degree of integration of semiconductor integrated circuit in recent years, the necessity of the formation of fine patterns is being increased, in which the electron beam lithography technique, and a resist material and a process technique capable of being used therefore are indispensable.
One of the problems in the electron beam lithography is that the throughput is inferior to the lithography technique using a stepper. While improvement of the apparatus including the exposure system are necessary for improving the throughput, improvement of the sensitivity of the photoresist is also an important factor. As simple mathematics, the throughput can be improved twice if the sensitivity is increased twice.
The electron beam lithography involves a problem in contamination of an EB column upon EB writing a resist due to a vacuum system included in the apparatus. This is because of the following reasons. In recent years, material referred to as a chemical amplification type is used as a photoresist for the electron beam lithography from the standpoint of sensitivity. The material, in the case of a positive type, has an alkali soluble group, such as a hydroxyl group, protected with a substituent capable of being decomposed with an acid. As the substituent in the conventional resist materials, a tert-butoxycarbonyl group, a tert-butyl group, a trimethylsilyl group, an ethoxyethyl group and the like have been used. These protecting groups are released and vaporized into vacuum with an acid generated upon EB writing even in a room temperature atmosphere in the EB column. The hydrocarbon thus formed deteriorates the vacuum in the mirror tower to cause failures in the exposure system.
Furthermore, photoresists used in photolithography of the next generations necessarily have a smaller thickness for avoiding a problem in incident distance of incident electrons, a problem in resolution, and particularly, collapse of patterns. There is such a problem, associated therewith, that the etching selectivity is difficult to ensure in the subsequent processing step of a substrate, and thus a photoresist, which has an alicyclic protecting group, improved with etching resistance has been proposed (for example, in J. Photopolym. Sci. & Technol., vol. 16, No. 3, p. 455-458 (2003)).